The Human T-lymphotropic virus Type I (HTLV-1) is a humanRNAretrovirus that causes T-cellleukemia and T-cell lymphoma in adults and may also be involved in certain demyelinating diseases, including tropical spastic paraparesis. The HTLV-1 genome is diploid, composed of two copies of a single-stranded RNA virus whose genome is copied into a double-stranded DNA form that integrates into the host cell genome, at which point the virus is referred to as a provirus. Adult T-lymphotropic virus (ATLV) is a strain of this disease that affects primarily adults. A closely related virus is bovine leukemia virusBLV.

HTLV-II

HTLV-III and HTLV-IV

The terms "HTLV-III" and "HTLV-IV" have been used to describe recently characterized viruses.[1][2][3]

These viruses were discovered in 2005 in rural Cameroon, and were apparently transmitted from monkeys to hunters of monkeys through bites and scratches.

HTLV-III is similar to STLV-III (Simian T-lymphotropic virus 3).[citation needed] Multiple strains have been identified.[4] It expresses gag, pol, and env, among other proteins.[5]

HTLV-IV does not resemble any known virus.

It is not yet known how much further transmission has occurred among humans, or whether the viruses can cause disease.

The use of these names can cause some confusion, because the name HTLV-III was the former name of HIV in early AIDS literature, but has since fallen out of use.[6]. The name HTLV-IV has also been used to describe HIV-2.[7]